Oscillator circuit having a stable output signal resistant to power supply voltage fluctuation

Abstract

A stable frequency is outputted by an oscillator circuit including a constant current circuit which is electrically connected between a first terminal and a second terminal, a voltage controlled oscillator circuit in which an oscillation frequency fluctuates in accordance with a potential difference between power supply voltage terminals, an n-channel transistor, a p-channel transistor in which a gate-source voltage is set to be constant by the constant current circuit, and a capacitor, in which a source electrode of the p-channel transistor is electrically connected to the first terminal, a drain electrode of the p-channel transistor is electrically connected a drain electrode and a gate electrode of the n-channel transistor, a source electrode of the n-channel transistor is electrically connected to the second terminal, and a gate electrode of the n-channel transistor is electrically connected to the second terminal through the capacitor.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an oscillator circuit and a semiconductor device including the oscillator circuit.[0003]2. Description of the Related Art[0004]In recent years, semiconductor devices in each of which various circuits are integrated on one insulating surface have been developed. As a clock circuit necessary for a circuit, various oscillator circuits are known.[0005]Oscillator circuits have been developed using CMOSs, and an oscillator circuit using a CMOS inverter is given as a typical example (for example, Patent Document 1: Japanese Published Patent Application No. 2003-283307).SUMMARY OF THE INVENTION[0006]However, a conventional oscillator circuit has the following problem. When a power supply voltage supplied to an oscillator circuit fluctuates, the value of a current flowing through an inverter is changed and thus an oscillation frequency is changed. Therefore, in a case where an output from the osc...

AI Technical Summary

Benefits of technology

The present invention provides an oscillator circuit that suppresses fluctuations in its oscillation frequency due to changes in power supply voltage or wireless signals. The circuit includes a constant current circuit, a voltage controlled oscillator circuit, and a capacitor. The constant current circuit provides a constant current regardless of changes in power supply voltage, while the voltage controlled oscillator circuit changes its frequency in response to changes in the voltage. The capacitor helps to stabilize the frequency. The invention also includes an improved version of the circuit that further reduces fluctuations in the frequency. Overall, the invention provides an oscillator circuit that is more stable and reliable for use in various semiconductor devices.

Problems solved by technology

However, a conventional oscillator circuit has the following problem.

Therefore, in a case where an output from the oscillator circuit is used as a clock signal, if the oscillation frequency fluctuates, the clock signal is changed, resulting in a circuit malfunction.

An oscillation frequency is easily affected by a ripple of a power supply voltage or a noise due to a wireless signal; therefore, it is difficult to stabilize an oscillation frequency.

Images